The Wnt family of genes encode over twenty cysteine-rich, secreted glycoproteins that act by binding to Frizzled (Fzd) receptors on target cells. Binding of Wnt to Fzd can initiate signaling by one or several pathways. In the termed canonical pathway, activation of Disheveled leads to the inactivation of Glycogen syllthase lcinase-3β (GSK-3p), a cytoplasmic serine-threonine kinase. The gsk-3β target, β-catenin, is thereby stabilized and translocates to the nucleus where it activates TCF (T-cell-factor)-dependant transcription of specific promoters (Wodarz, 1998; Dierick, 1999). In the non-canonical or planar tissue polarity pathway, binding of Wnt to Fzd also activates Disheveled (Krasnow et al., (1995). Development 121,4095-4102) which in this case activates RhoA, a small g protein (Strutt et al., (1997). Nature 387, 292-295). RhoA then signals through JNK (Jun N-terminal lcinase) and Rock (Rho associated Kinase) (Boutros et al., (1998). Cell 94,109-118) to regulate cytoskeletal dynamics during gastrulation. Wnt proteins are also known to signal through modulation of intracellular calcium. This is thought to activate Protein Kinase C (PKC) (Sheldahl of al., (1999). Curr. Biol. 9,695-698) and leads to the nuclear translocation of the transcription factor NFAT. Recently, it has been determined that the Wnt signalling pathways are capable of directing cell fate determination in various tissues, including kidney (Labus, 1998 Vainio, 2000), CNS (Patapoutian, 2000), hematopoietic (Van Den Berg, 1998), and skeletal muscle (Cossu, 1999). Wnt signalling has also been implicated in postnatal wound healing and tissue regeneration in zebrafish and hydra (Hobmayer, 2000; Labus, 1998; Poss, 2000).
The involvement of Wnt signalling in the proliferation or differentiation of hematopoietic stem cells derived from fetal tissue or bone marrow has also been described. For example, U.S. Pat. Nos. 5,851,984 and 6,159,462 describe the use of Wnt polypeptides for enhancing the proliferation, differentiation and/or maintenance of hematopoietic stem or progenitor cells and U.S. Pat. No. 6,465,249 describes the use of β-catenin for the in vitro expansion of progenitor or stem cells, in particular hematopoietic stem cells. U.S. Pat. No. 6,165,748 describes novel proteins, the Frazzled proteins, which are involved in the Wnt signalling pathways and their use to induce expression of factors in and/or differentiation of tissues and organs. Canadian Patent Application No. 2,353,804 describes the use of Wnt3a to stimulate myogenesis in P19 embryonal carcinoma cells and suggests that myogenesis may be controlled by modulation of Wnt activity, in particular that myogenesis may be inhibited by inhibition of a Wnt polypeptide.
U.S. Patent Application No. 20030040051 describes a set of novel members of the vertebrate Frizzled family of genes and methods of screening for compounds that affect the binding of a Wnt to the polypeptides encoded by these genes.
Stem cells have the potential for providing benefit in a variety of-clinical settings but a number of limitations to many potential applications have been encountered including, for example, obtaining a sufficient number of target cells and stimulating terminal differentiation of these stem cells into mature, tissue specific cells.
There is a need in the art for methods and compositions that are capable of modulating the growth, differentiation or both growth and differentiation of stem cells.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
It is an object of the invention to overcome disadvantages of the prior art.
The above object is met by the combinations of features of the main claims, the sub-claims disclose further advantageous embodiments of the invention.